Kommentar zu Bereschit 29:12

כי אחי אביה הוא HE WAS HER FATHER’S BROTHER — near kin to her father, as (Genesis 13:8) “for we are men, brothers (אחים)” (i. e. near kin). A Midrashic explanation is that he meant: if he (Laban) intends to practice deceit upon me then I am his brother (a match for him) in deception; if, however, he is an honest man then I, too, am the son of his sister, the pious Rebekah (Genesis Rabbah 70:13).

AND SHE TOLD HER FATHER. Rashi comments: “Her mother was dead.” And so it is stated in Bereshith Rabbah.⁷⁴70:12. But according to the plain meaning of Scripture, Rachel related it to her father in order to inform him of the arrival of his relative and so that he should go forth to meet him and honor him. For, as regards her mother, what was Jacob to her and what could she do for him? However, Rebekah did show her mother the jewels which Eliezer gave her,⁷⁵Above, 24:28. as is the custom of maidens.

כי אחי אביה הוא, the Torah adds this at this point to justify his kissing Rachel and her allowing herself to be kissed by him.